2.0 Analysis 2.1 Certification The builder of the accident aircraft was also the manufacturer's designated Industry Representative for the Cuby II aircraft. There was, therefore, no requirement for independent supervision of the aircraft's construction, or for an independent final check of the aircraft before it was certified for flight. 2.2 Centre of Gravity There is no record of the aircraft's C of G before the aircraft was painted, and it could not be determined how much paint was applied in the second coat. However, because the fuselage and part of the tail were found to have thicker paint than the rest of the aircraft, and the repainted part of the aircraft is mostly aft of the C of G, repainting the aircraft had the effect of moving the C of G aft. The C of G calculation found with the aircraft documents was not dated and so it is not possible to determine whether it was prepared before or after the repainting, the relocation of the battery, or the addition of the ballast weight to the engine. However, because those changes would not have been sufficient to move the C of G within the required range, the C of G of the aircraft was probably beyond the aft limit at the time of the accident. 2.3 Aileron Gap Seals In the construction manual, the tape aileron gap seals are mentioned in the Aileron Section diagram by the reference: Seal gap with tape after final assembly. See instr. book. The manufacturer reportedly advised the builder to install the tape gap seals. The seals are not described in the text of the construction manual. The manufacturer advises that tape gap seals are required to reduce turbulence around the ailerons and improve lateral stability. Because the accident aircraft lacked tape gap seals, its lateral stability was reduced. 2.4 Effect of the Weather The wind speed increased during the stopover in Davidson and by 1600 CST the wind was 11 knots gusting to 18 knots. Witnesses noted variable and buffeting winds and observed numerous dust devils along the aircraft's flight path. Since wind gusts as high as 37 knots above ambient wind have been observed in dust devils, and the accident aircraft's cruise speed was about 25 to 30 knots higher than its stalling speed, wind shear in a dust devil could have reduced the airspeed of the accident aircraft below its stalling speed. 2.5 Aerodynamic Stall and Spin Because the aft C of G reduced the aircraft's pitch stability, reduced its elevator effectiveness, and increased the aircraft's susceptibility to aerodynamic stall, the pilot was probably unable to avoid stalling the aircraft when it encountered gusty winds and possibly dust-devil-related wind shear. Because of the effects of the aircraft's lack of tape aileron gap seals and its aft C of G, the pilot was probably unable to maintain control of the aircraft in the stall. Once the aircraft stalled, it entered a spin from which recovery was not possible in the altitude available. 2.6 Engine and Propeller The damage to the propeller indicates that the engine was operating at low power at impact. However, because there was no evidence of a malfunction, it is unlikely that either the engine or propeller was a factor in this occurrence. 2.7 Survivability Despite the failure of the occupant restraint system, the accident was not survivable because of the high deceleration forces and crushing of the occupant compartment. 3.0 Conclusions 3.1 Findings The aircraft records indicate that it was certified and equipped in accordance with existing regulations and approved procedures. There was no requirement for independent supervision of the aircraft's construction, or for an independent final check of the aircraft before it was certified for flight. The pilot was certified and qualified for the flight in accordance with the Transport Canada Ultralight Aeroplane Policy. The C of G of the aircraft was probably beyond the aft limit at the time of the accident. There was no evidence that incapacitation or physiological factors affected the pilot's performance. The lack of tape gap seals probably reduced the effectiveness of the ailerons, thereby reducing the lateral stability of the aircraft. The aircraft encountered gusty winds and wind shear which probably exceeded the capabilities of the aircraft. The aircraft stalled and entered a spin from which recovery was impossible in the altitude available. The accident was non-survivable because of the high deceleration forces and crushing of the occupant compartment. 3.2 Causes The aircraft encountered gusty winds and wind shear which probably exceeded its capabilities, then stalled and entered a spin from which recovery was impossible in the altitude available. Contributing factors were the aft centre of gravity of the aircraft and incomplete aileron gap seals. 4.0 Safety Action 4.1 Action Taken The manufacturer has amended the text of the aircraft's construction manual to describe the installation of the tape gap seal, and has added a diagram illustrating both types of gap seals in detail.